1. Field of the Invention
The present invention is related to a technique for detecting a forming position of an output image in an image forming apparatus such as a copying machine and a printer and for adjusting an image forming position based upon the detection result, and also related to a technique for detecting photographic density, colors, and gradation of an output image in the image forming apparatus and for controlling an image forming condition based upon the detection results.
2. Description of the Related Art
Image qualities of image forming apparatus are conspicuously improved, and in connection with this image quality improvement, sever requirements are made by users with respect to variations in image qualities of color images. As a result of investigation made by the Inventors, such image qualities near limitations of human color discriminating capabilities are required, for instance, a color difference lower than, equal to 3 is required. Also, sever requirements with respect to color shifts are made by users, for example, color shifts must be lower than, or equal to 100 to 200 μm.
In particular, among electrophotographic type color image forming apparatus and the like, which have employed electrophotographic processes, variations in image qualities known as image density, positional shifts of respective color toner images, color reproducibilities, gradient characteristics, and photographic fog, may constitute problems to be solved. In such an electrophotographic type color image forming apparatus, while an electrostatic latent image is formed on a photosensitive member, this electrostatic latent image is developed by a toner so as to form a toner image on the photosensitive member, and then, this toner image is directly transferred to a recording medium, or is transferred via an intermediate transfer member to the recording medium, and thereafter, this transferred toner image is fixed on the recording medium. This problem is mainly caused by that an image quality reproducibility of an electrophotographic process is adversely influenced by such an environmental condition as a temperature and humidity, and also deteriorations by aging effects.
With respect to the above-described problem, such an image forming system has been widely used in which reflection light of light illuminated to an image quality controlling reference pattern image formed on an image carrier is sensed by an optical type photosensor so as to perform both an image density adjusting operation and a positional adjusting operation based upon the sensor output. Another image forming apparatus has been proposed (JP-A-2000-47447). In this image forming apparatus, while both density changes and positional shift amounts of reference pattern images in yellow, magenta, cyan colors are detected by a photosensor, which have been formed on a image carrier, both the image forming density and the positional shift are controlled every color component based upon this detection result. In addition, as the photosensor, such a photosensor apparatus used in an image forming apparatus has been proposed (JP-A-2000-250304). That is, while both a regular reflection type and a diffuse reflection type are combined to be conducted to a photosensor apparatus, this photosensor apparatus is applied to the image forming apparatus so as to control both image forming density and a positional shift. In the regular reflection type photosensor, regular reflection light reflected from a black toner image is sensed, and thus, density is detected in a higher sensitivity. In the diffuse reflection type photosensor, while diffuse reflection light reflected from the respective reference pattern images is sensed, density up to high density can be detected.
On the other hand, when density is detected by employing a photosensor, there is such a problem. That is, a wide detecting visual field with respect to diffuse reflection light where reflection light is diffused must be secured, as compared with a detecting visual field when regular reflection light is detected. As a consequence, in a conventional sensor optical system, sizes of reference pattern images for yellow, magenta, and cyan colors, which reflects light in a diffuse reflection mode, cannot be made smaller than a size of a reference pattern image for a black color, which reflects light in a regular reflection mode. As a result, there is such a drawback that in order to form the above-described reference pattern images for these three colors, a larger amount of toners are required, as compared with an amount of toners used to form the reference pattern image for the black color, and furthermore, extra toners are consumed so as to perform adjusting process operation.
Further, another method has been proposed by employing a single photosensor in order also detect a position (registration detection) However, even in such a case that a diffuse system is employed by which an adverse influence of a mounting angle error of the photosensor is reduced, since a visual field required to detect diffuse reflection light becomes wide, there is another problem that position detecting precision is deteriorated. As a consequence, a requirement of such a technical idea has been made, by which the visual field required to detect the diffuse reflection light may be made substantially equal to the visual field required to detect the regular reflection light.
In response to this requirement, another method has been proposed (JP-A-2002-244371). This proposed method limits the visual fields with respect to the diffuse reflection system and the regular reflection system. However, in such a case that this proposed method is applied, two sorts of sensors are required, namely, both the diffuse reflection-purpose sensor and the regular reflection-purpose sensor are required, so that total cost of these sensors becomes twice. Furthermore, in such a case that these two sorts of sensors are simply combined with each other, two sorts of light receiving optical systems corresponding to both the diffuse reflection light and the regular reflection light are required. This may cause the complex structure of the photosensor apparatus, and the cost reducing effect would be decreased.